Suction brake, sheet conveyor with such suction brake and method of applying a retardation force to a moving sheet of material

ABSTRACT

The invention relates to a suction brake for use with a sheet conveyor configured to convey a succession of flat elements in sheet form along a conveying path between a first location and a second location, the suction brake comprising:a hollow body having an interior cavity and a face that defines a plurality of suction apertures that communicate with the interior cavity;an obturator arrangement coupled to the hollow body and moveable with respect to the suction apertures;the obturator arrangement being moveable between an open position, in which the obturator arrangement exposes the suction apertures to a maximum extent, and a restricted position, in which the obturator arrangement occludes the suction apertures to a maximum extent. The obturator may rotate or be linearly translated in moving between the open and restricted positions.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a National Stage under 35 U.S.C. § 371 ofInternational Application No. PCT/EP2020/065218, filed on Jun. 2, 2020,which claims priority to European Patent Application No. 19020363.8,filed Jun. 5, 2019, the contents of all of which are incorporated byreference in their entirety.

The present invention relates to a suction brake for use with a sheetconveyor, to a sheet conveyor having such suction brake and to a methodof applying a retardation force to a moving sheet of material using asuction brake.

The invention finds a particularly advantageous, although not exclusive,application in the field of the manufacture of packaging made of paperor light cardboard.

In the packaging manufacturing industry, packaging is made from a sheetof cardboard generally in several steps. This is why known processingmachines of the prior art are traditionally made up of severalsuccessive workstations through which each sheet is moved sequentially.In practice, each sheet is conveyed individually from one workstation toanother by pulling it via its front edge, typically using what is knownas a gripper bar, leaving the rest of the sheet not held in anyparticular way.

In order for the sheet nonetheless to maintain a certain degree offlatness as it decelerates from the maximal feeding speed on arriving ata workstation, it is known practice to brake its rear portion during thesheet introduction phase by using a suction bed which may be referred toas a suction braking device or suction brake. Installed transversely inclose proximity to the entry to the workstation, such a braking deviceperforms its function by restraining the rear portion of the sheet usingsuction, while at the same time allowing it progressively to slide asits front portion is pulled forward. In particular, when a sheet arrivesat a workstation for processing, the gripper bar that is pulling thefront edge of the sheet stops to enable the sheet to be processed. Thesuction brake is used to generate friction between the sheet and astationary surface, thereby providing a braking effect on the trailingparts of the sheet, so that the inertia of the sheet does not cause thesheet to buckle, crumple or crease. Any or all of the workstations mayinclude a suction brake.

Suction for a suction brake may be provided by using one or more suctionpumps to evacuate the interior air/gas of the braking device, therebyresulting in suction at suction apertures of the device. An alternativeis a Bernoulli device in which suction is provided using the Venturieffect by forcing gas under pressure within the braking device toaccelerate through a restriction. The suction apertures of the brakingdevice communicate with one or more cavities of the device within whichthe Venturi effect operates. Because the Venturi effect enableslocalised generation of suction, is energetically very efficient, andbecause it is easy both to provide a supply of pressurised gas, e.g.compressed air, and to deliver this wherever it is required, in practicethe use of a Bernoulli device rather than one relying on an externalsource of suction is generally preferred.

In operation, a suction brake first sucks out the air between the sheetand an operating surface of the braking device, and then, by pulling thesheet against the operating surface of the device, applies a restrainingforce to the sheet that serves as a braking force. Ideally the firstoperation of sucking out the air between the sheet and the operatingsurface of the braking device is achieved as quickly as possible so asto avoid sheet deformation as the result of sheet inertia. This requiresmaximum suction. With a Bernoulli device this implies the use ofsignificant amounts of high pressure compressed gas.

In the second stage of operation, the sheet is sucked to the operatingsurface of the braking device, blocking the suction apertures, and theair flow through the suction apertures drops to zero. The sheet is stilldecelerating at this stage, and the braking force applied has to be highenough to be able to brake the sheet effectively, avoiding the formationof ripples in the sheet and keeping the sheet flat. Optimal performance,and in particular avoiding sheet distortion, requires the amount ofsuction at this second stage to be adjusted based on the type of sheet(e.g. the material type of the sheet, and its weight) as well as thecutting shape of the sheet. This means that the pressure and/or volumeof gas that is fed to the Bernoulli device needs to be adjusted based onthe requirements of this second stage of operation—even though that mayconflict with the requirements of the first stage. Applying too high abraking force at this stage of the operation may cause machineinterruptions, damage to packaging blanks, etc.

The restrictions in gas pressure/volume required for the second stage ofthe operation may mean that the first stage of the operation proceedstoo slowly, with the consequence that the speed of the transport systemand/or the cadence of the processing machine needs to be reduced toreduce the burden on the braking system (by reducing the amount of speedthat has to be shed and/or by providing a longer interval for the firststage of the operation to be performed—so that the sucked air flow ratecan be lower). Also, with a lower cadence, less sheet deceleration isrequired, and thus the magnitude of the restraining force required isalso reduced. But the disadvantage of this is that there iscorresponding reduction in throughput and hence decreased productivity.

It would be desirable if the conflicting demands of the first and secondstages of the braking operation could be reconciled without aconcomitant reduction in operating speeds and throughput, while avoidingblank damage and machine/production line stoppages.

According to a first aspect, the present invention provides a suctionbrake for use with a sheet conveyor configured to convey a succession offlat elements in sheet form along a conveying path between a firstlocation and a second location, the suction brake comprising:

-   -   a hollow body having an interior cavity and a face that defines        a plurality of suction apertures that communicate with the        interior cavity;    -   an obturator arrangement coupled to the hollow body and moveable        with respect to the suction apertures;    -   the obturator arrangement being moveable between an open        position, in which the obturator arrangement exposes the suction        apertures to a maximum extent, and a restricted position, in        which the obturator arrangement occludes the suction apertures        to a maximum extent,    -   wherein the hollow body comprises a Bernoulli device and the        suction orifices are provided by the Bernoulli device.

This aspect of the invention enables the suction experienced by thesheet material during the second stage of the braking process to beregulated independently of the suction force applied during the initialphase. Thus the sucked gas flow rate during the initial phase can bemaximised while the degree of suction and hence braking force providedduring the second phase can be adjusted and set to the optimum levelbased on the size, nature and configuration of the sheets beingprocessed.

According to a second aspect, the present invention provides a sheetconveyor system configured to convey a succession of flat elements insheet form along a conveying path between a first location and a secondlocation, having a suction brake as defined above, the suction brakebeing arranged to apply a restraining force to trailing edges of flatelements being conveyed by the system.

This aspect of the invention also enables the suction experienced by thesheet material during the second stage of the braking process to beregulated independently of the suction force applied during the initialphase during, for example, a stamping operation. Thus the sucked gasflow rate during the initial phase can be maximised while the degree ofsuction provided during the second phase can be adjusted and set to theoptimum level based on the size, nature and configuration of the sheetsbeing processed.

According to a third aspect, the present invention provides a method ofapplying a braking force to a moving sheet of material using a suctionbrake having a suction orifice, the method comprising:

-   -   using the suction orifice to withdraw air from between the sheet        of material and a surface of the suction brake; and subsequently    -   throttling the suction orifice to reduce a free area of the        suction orifice; and    -   subsequently using the reduced free area of the suction orifice        to continue suction between the sheet and the surface of the        suction brake to cause the sheet to adhere to the surface.

This aspect of the invention enables the suction experienced by thesheet material during the second stage of the braking process to beregulated independently of the suction force applied during the initialphase. Thus the sucked gas flow rate during the initial phase can bemaximised while the degree of suction provided during the second phasecan be adjusted and set to the optimum level based on the size, natureand configuration of the sheets being processed.

According to another aspect, the present invention provides a suctionbraking device for use with a sheet conveyor configured to convey asuccession of flat elements in sheet form along a conveying path betweena first location and a second location, the suction braking devicecomprising:

-   -   a hollow body having an interior cavity and a face that defines        a plurality of suction apertures that communicate with the        interior cavity;    -   a throttling arrangement coupled to the hollow body and moveable        with respect to the suction apertures;    -   the throttling arrangement being moveable between an open        position, in which the throttling arrangement exposes the        suction apertures to a maximum extent, and a restricted        position, in which the throttling arrangement restricts the        suction apertures to a maximum extent.

Embodiments of the invention will now be described, by way of exampleonly, by reference to the accompanying drawings, in which:

FIG. 1 illustrates a foil stamping machine in which a suction brakeaccording to an embodiment of the invention is incorporated as part of asheet processing machine;

FIG. 2 shows, in detail, the sheet processing machine with which thefoil stamping machine shown in FIG. 1 is provided.

FIG. 3 is a cross section through a suction brake according to anembodiment of the invention;

FIG. 4 illustrates schematically the operation of a suction brakeaccording to an embodiment of the invention; and

FIG. 5 is a schematic plan view of part of a suction brake according toanother embodiment of the invention.

In the following description, the same elements have been denoted byidentical references. Only those elements that are essential tounderstand the invention have been depicted, and have been soschematically and not to scale.

In order to provide a context within which to describe embodiments ofthe invention, first a conventional sheet processing machine isdescribed, with which a suction brake according to an embodiment of theinvention can be provided. FIG. 1 therefore illustrates a sheetprocessing machine 100 that uses stamping to customize cardboardpackaging intended for the luxury goods industry. Such a processingmachine, commonly referred to as a foil stamping machine, is known inthe prior art. It will therefore not be described in detail here, eitherin terms of its structure or in terms of its operation. Moreover, forease of description and ease of understanding only one station of thesheet processing machine is described as including a suction brake, butthe skilled person will understand that more than one station mayinclude a suction brake. Also, of course, although the station describedas having a suction brake is a stamping station, suction brakesaccording to embodiments of the invention find application with otherstations of sheet processing machines, for example with a reception areaor an ejection area, and are in no way limited to use with stampingstations.

This sheet processing machine 100 is made up in the conventional way ofseveral workstations 110, 120, 130, 140, 150 which are juxtaposed toform a unit assembly capable of processing a succession of flat elementsin sheet form. Thus, the entry to the machine comprises a sheet feeder110, performing the function of feeding the machine, sheet by sheet,from a stack, followed by a feed table 120, on which the sheets are laidout in a stream before repositioning one sheet after the other withprecision.

Next is a stamping station 130 which uses a platen press 131 to apply toeach sheet, a hot foil stamping, metalized coating which comes from astamping foil 141. The actual stamping operation itself takes placebetween an upper platen 132, which is static, and a lower platen 133,which is mounted with the ability to move vertically up and down. Asuction brake 134 according to an embodiment of the invention findsparticular application in providing a braking and restraining effect tosheets being decelerated for being stamped, as will be describedsubsequently.

The next module in the machine 100 comprises a foil feed and recoverystation 140. The purpose of this station is to deliver the foil 141which is stored wound around a feed reel 142, then to recover it bywinding it around a recovery reel 143 once it has been used afterpassing through the platen press 131. Between the point at which it isstored and the point at which it is recovered, the foil 141 is drivenalong by a drive system 144. This system is mainly made up of a seriesof turn bars 145, which are installed along the path followed in orderto guide the movement of the foil 141, and of a combination of a feedshaft 146 and of a press roller 147 which are positioned downstream ofsaid path so that they can pull the foil 141 along.

The sheet processing machine 100 ends with a delivery station 150 inwhich the sheets, which arrive one after another, are reformatted into astack 151. To do that, the conveying means 160 which have the task ofpulling the sheets individually from the exit from the feed table 120 asfar as the delivery station 150 are moreover arranged so that theyautomatically release each sheet once the latter has come into line withthe stack 151 which is in the process of being formed in the deliverystation 150. Conventionally, these conveying means 160 use a series ofgripper bars 161 which are mounted with the ability to effect atransverse translational movement, via two sets of chains 162 arrangedlaterally one on each side of the sheet processing machine 100.

FIG. 2 illustrates a similar foil stamping machine 200 to the oneillustrated more schematically as 130 and 140 in FIG. 1 . In thisstamping machine 200, the foil in the foil feed and recovery station 140passes through the machine in the opposite direction to the passage ofthe sheets being stamped (unlike in FIG. 1 )—either direction beingequally useable. The stamping machine 200 is likewise provided with aplaten press 131. In this particular embodiment, chosen solely by way ofexample, stamping is done between a heating upper platen bolster 211which is fixed, and a lower platen bolster 212 which is mounted so thatit can move in a reciprocating vertical movement. The heating upperplaten bolster 211 supports a frame 213 under which stamping blocks, notvisible here, are fixed, while the lower platen bolster 212 carries astamping plate 214 to which stamping counterparts, likewise not visible,are attached.

The foil stamping machine 200 is also provided with unwinding means 230to feed the platen press 131 with stamping foil 141 which is in the formof a strip. As is conventional, these unwinding means 230 comprise areel holder 231 with respect to which a reel 210 of stamping foil ismounted so that it can rotate, a feed shaft associated with pressrollers 232 a, a mark detector 233, a series of return shafts 234 a, 234b, 234 c, a strip breakage monitor 235, a tensioning shaft associatedwith press rollers 236 a, a strip return 237, and a recovery roller 238.

To supplement these unwinding means 230, introduction means 250 are alsoprovided to position the stamping foil 141, and in particular to causeit to pass through the platen press 131. To do that, the introductionmeans 250 have a loader bar 251 which is mounted transversally mobile intranslational movement between the two platen bolsters 211, 212 and,more generally, about the heating upper platen bolster 211. Just likethe strip unwinding means 230, the sheet introduction means 250, areconventional.

Finally, the sheet processing machine 100 comprises a transportarrangement 240 allowing each sheet 10 to be moved individually from theexit of the feed table 120 as far as the delivery station 150, includinginto the platen press 131. The position of a sheet within the sheetprocessing machine, that effectively defines the conveying path of asheet through the sheet processing machine, is indicated by thereference 10* in FIG. 2 . It will be seen that the sheet 10* ispositioned between the upper and lower platen bolsters 211 and 212.

As can be seen, the transport arrangement 240 use a series of gripperbars 241 which are mounted with the ability to move transversally intranslational movement via two sets of chains 242 positioned laterallyon each side of the foil stamping machine. Each set of chains 242 runsin a loop which allows the gripper bars 241 to follow a path that passesin succession via the platen press 131, the feed and recovery station140 and the delivery station 150.

In concrete terms, each gripper bar 241 performs an outbound path in ahorizontal passage plane between a drive sprocket 243 and a returnsprocket, then a return path guided by rollers (not visible) in theupper part of the foil stamping machine. Once it has returned to thevicinity of the drive sprocket 243, each gripper bar 241 is then capableof taking hold of a new sheet 10 as shown in FIG. 2 .

FIG. 2 also shows that each gripper bar 241 consists of a transverse bar245 on which a plurality of grippers 246 are mounted, the grippers beingdesigned so that they can take hold of the front edge of one and thesame sheet 10 simultaneously. It will also be noted that each gripperbar 241 is coupled to the two sets of chains 242 via the two respectiveends of its transverse bar 245.

The sheet processing machine 100 further comprises a suction brake 134,according to an embodiment of the invention, that is able to partiallyrestrain each sheet 10 by its rear portion, and do so during the phaseof introduction of the sheet 10 into the platen press 131. The suctionbrake 134 is able to hold the rear portion of each sheet 10 roughly inthe plane of travel of its front edge, during the phase of introductionof said sheet 10 into the platen press 131.

The suction brake 134 comprises a suction member 261 which is positionedupstream of the platen press 131, and which is capable of collaboratingthrough sliding contact with the rear portion of each sheet 10 beingintroduced into said platen press 131. Associated with the face of thesuction brake 134 is an obturator arrangement 262 that will come intocontact with the sheet 10 and which is operable to provide a throttlingaction to suction orifices, not shown, in the suction member. Thefunction and operation of the obturator arrangement 262 will bedescribed in more detail with reference to FIGS. 3 and 4 .

According to a preferred embodiment of the invention, the suction member261 is fixed, and is positioned as close as possible to the pathfollowed by the front edge of each sheet 10 just before it is actuallyintroduced into the platen press 131. Such a layout specifically allowsthe suction member 261 to be systematically in contact with any sheet 10being introduced into the platen press 131. It also has the advantage ofguaranteeing that the sheet is positioned roughly parallel to theinternal faces of the platen bolsters 211, 212.

In this exemplary embodiment, each sheet 10 is pulled by a gripper bar241 as it is introduced into the platen press 131. In concrete termswhat this means is that the suction brake 134 is positioned in thedirect vicinity of the path followed by said gripper bar 241 as itapproaches the platen press 131.

However, according to an alternative form of embodiment that has notbeen depicted, the suction brake 134 could also be mounted such that itis able to move between an active position and a passive position. Theassembly would then be arranged in such a way that, in the activeposition, the suction brake 134 was positioned as close as possible tothe path followed by the front edge of each sheet 10 just before it isintroduced into the platen press 131, and so that, in the passiveposition, it is positioned some distance away from said path. Of course,the sheet processing machine 100 would then comprise means capable ofmoving the suction member 134 from the passive position into the activeposition when the sheet 10 is ready to be introduced into the platenpress and, conversely, of moving said suction brake 134 from the activeposition into the passive position when said sheet 10 is extracted fromthe platen press.

According to one particular feature of this alternative form ofembodiment, with the platen press being capable of stamping each sheet10 between a fixed platen and a moving platen, the suction brake 134 issecured to the moving platen; said moving platen then forming the meansof movement.

According to one embodiment, with the hot stamping of each sheet 10being performed on a given face, known as the application face, thesuction brake 134 is positioned on the opposite side to said applicationface; said sheet 10 being considered as it approaches the platen press131. It must nonetheless be understood that it is still entirelypossible for the suction brake 134 to be installed on the same side asthe application face.

According to a preferred embodiment, the suction brake 134 operatescontinuously. Be that as it may, it is perfectly conceivable for thesuction brake 134 to be operated discontinuously. In such an event, thesheet processing machine 100 will be arranged in such a way that thesuction brake 134 is activated as soon as the front edge of a sheet 10arrives plumb with it and is deactivated as soon as the rear of saidsheet 10 is no longer in contact with said suction brake 134.

In a particularly advantageous manner, the suction brake 134 acts overroughly the entire width of each sheet 10 being introduced into theplaten press 131.

According to a currently preferred embodiment of the invention, thesuction brake 134 is of the Bernoulli type, that is to say is a deviceprovided with at least one suction hole (suction orifice) where a vacuum(arrow f1 in FIG. 3 ) is created through a Venturi effect, by drivingair under pressure through a discharge pipe (arrows f2 in FIG. 3 ) whichcommunicates laterally with the suction hole and which is provided witha restriction upstream of said suction hole.

FIG. 3 shows a cross-section through the suction brake 134. As shown inFIG. 3 , the suction brake 134 consists of a tablet 362 through which amain pressurized air supply channel 363 is formed longitudinally andcommunicates with at least one secondary channel 364 runningtransversally and opening to the rear of the tablet 362 via anindividual discharge orifice 365 (arrow f3). The secondary channel 364is formed between the upper face (as illustrated) of the main body ofthe tablet that provides the air supply channel 363, and a secondaryelement 368, here shown in the form of a plate, that overlies and isattached to the main body. Moreover, each secondary channel 364 on theone hand also communicates with a suction orifice 366 which opens ontothe face of the tablet 362 which would, were it not for the presence ofobturator arrangement 262, come into contact with each sheet 10 beingintroduced into the platen press 131. That face is provided by the upper(as illustrated) face of the secondary element 368. Finally, eachsecondary channel 364 has a restriction 367 positioned just upstream ofthe suction orifice 366. It is understood here that the terms“longitudinally” and “transversally” mean with respect to the body ofthe tablet 362, whereas the term “rear” is to be understood in relationto the direction of travel of the sheets 10 (arrow 4), and “upper” is tobe understood as towards the path of travel of the sheets.

Preferably, as shown, each discharge orifice 365 is directed inopposition with respect to the platen press 131 and with respect to theplane of travel of each sheet 10 as it approaches the platen press 131.The objective here is for each discharge air flow (arrow f3) to bedirected in a direction that does not disturb the attitude of the sheets10 as they are introduced into the platen press 131.

Also preferably, as shown, each suction orifice 366 has a conical shapeopening out toward the outside, notably in the region of its portion 371closest to the platen press 131. The objective here is to prevent anycorner of the front edge of the sheet 10 from entering a suction orifice366 of the tablet 362 as the sheet 10 approaches the platen press 131.

FIG. 3 also illustrates the provision of an obturator body 262, here inthe form of a plate, which enables the selective throttling of thesuction orifice 366. As shown, the obturator arrangement is in the formof a plate that lies between the upper face (which might be consideredto be the working face) of the secondary element 368 and the path ofmovement of the sheet 10, the path being shown schematically by thearrow labelled f4.

The obturator body is displaceable with respect to suction orifice 366between an open position and a restricted position. In the openposition, a hole 369 in obturator body 262 is in register with thesuction orifice 366. As shown, the hole 369 in the obturator bodymatches the conical shape of the suction orifice 366. This configurationis optional but if used it can help to avoid loss of suction when theobturator arrangement is fully open, which is desirable.

In order to avoid wasting available suction, it is preferred to providea seal between the mating surfaces of the obturator element and thecooperating surface of the suction brake, e.g. by providing an O-ringaround the rear of the hole 369 in the obturator body, as indicated by370.

To achieve a throttling effect, the obturator body is moveable withrespect to the suction orifice 366 so that the hole 369 moves out ofregister with the suction orifice, meaning that a portion of theobturator body adjacent the hole 369 starts to occlude the suctionorifice 366. Such position is referred to as a restricted position. Thegreater the relative movement between the obturator body and that partof the suction brake that defines the suction orifice, the greater thedegree of throttling and hence the greater the reduction in suction andtherefore the braking force experienced by the sheet during the secondstage of the braking operation. Accordingly, intermediate positionbetween the open position and the restricted position in which thethrottling effect is at a maximum, are possible.

Although FIG. 3 only shows one suction orifice 366 and one hole 369 inthe obturator body, those skilled in the art will appreciate that, inpractice, suction brakes according to embodiments of the invention mayhave multiple suction orifices and the obturator arrangement may beconfigured to enable throttling of all or most of the suction orificesprovided.

Having introduced the principle behind the operation of a suction brakeaccording to an embodiment of the invention, further aspects ofembodiment of the invention will now be described with reference to FIG.4 .

FIGS. 4 a and 4 b are perspective views of an embodiment of the suctionbrake showing a plurality of suction orifices (suction apertures) 366,and a plurality of holes 369 in the obturator body 262. The suctionbrake includes an obturator arrangement 262 which enables the suctionorifices to be selectively throttled to reduce the amount of suctionprovided. This enables the constraints of the first and second stages ofthe braking operation to be decoupled, so that high suction can bemaintained for the first stage and a suitably lower level of suctionprovided for the second stage according to the requirements of the sheetbeing handled. The throttling effect is achieved through relativemovement between the obturator arrangement and the suction orifices.

Preferably, the obturator apertures have the same size, and they areregularly spaced so as to achieve an even retarding effect on a sheet.

In FIG. 4 , the obturator arrangement comprises the obturator body inthe form of a slide 262 having holes 369 spaced and sized to match theopenings of the suction orifices 366 in what would otherwise be thesheet-contacting face of the suction brake. FIG. 4 a shows a firstposition, the fully open position, in which the holes 369 in the slidefully expose the openings of the suction orifices, so that effectivesuction provided by the suction brake, for a given supplied gas flow andpressure, is unaffected by the presence of the obturator arrangement.Thus, this fully open position is preferred for use during the firststage of the braking operation. But if less suction is required, forexample for the second stage of the braking operation, because of thenature of the sheets being processed, then the obturator arrangement canbe adjusted to reduce the effective size of the suction orifices asshown in FIG. 4 b . With the arrangement as shown in FIG. 4 , theobturator arrangement comprises an apertured slide, and this can bemoved laterally with respect to the suction orifices. This has theeffect of causing the body of the obturator arrangement to occlude thesuction apertures, because the apertures in the slide and the suctionorifices become (increasingly) misaligned—creating a throttling effect.By adjusting the extent of the movement of the obturator with respect tothe suction orifices, the extent of the throttling can be adjusted.

It will be noted that in FIG. 4 the obturator arrangement effectivelyoverlies the hollow body that carries the suction orifices, (although ofcourse the suction brake can be used in different orientations than theone shown, so that, for example, the hollow body could be “flipped” sothat the obturator arrangement is positioned beneath the hollow body) sothat the obturator is positioned between the hollow body and the paththat sheets to be processed will follow. Such an arrangement may beadded to an existing design of Bernoulli plate without requiring theinterior design of the venture system to be modified. While it may bepossible to provide an internal obturator arrangement where suction isprovided from an internal venture arrangement, there is clearly greaterdesign freedom to add an internal obturator arrangement in situationswhere suction is instead provided from an external suction source, suchas a vacuum pump.

It will be noted that in FIG. 4 the suction orifices and the aperturesin the obturator arrangement are elongate rather than circular. The longaxes of these elongate openings are arranged transverse to the feeddirection of the sheet material. This enables the area of each suctionorifice to be maximised without requiring a significant length of thesuction body along the feed direction.

In FIG. 4 , a crank arrangement 400 which converts a rotary movement,from a motor 410 for example, into linear movement (translation) of theslide 262 that forms the obturator arrangement. It will be appreciatedthat if the obturator arrangement is engaged, because of the nature ofthe sheets being processed, then the obturator arrangement will, duringthe processing of one sheet, reciprocate from the fully open position ofFIG. 4 a to an obstructive position, as shown in FIG. 4 b , and thenback again to the fully open position ready for the processing of thefollowing sheet.

The use of a crank arrangement 400, as generally shown in FIG. 4 , canprovide such a reciprocating movement simply and effectively. By usingan adjustable, or interchangeable crank, to achieve different crank“throws” the extent of the movement of the obturator arrangement withrespect to the suction orifices can be adjusted to suit thecharacteristics of different sheets being processed.

Instead of using a crank arrangement, the obturator arrangement could bemoved with respect to the suction orifices by means of one or morehydraulic or pneumatic rams, or an electrically powered solenoid, all ofwhich directly provide a linear movement suitable for translating, andreciprocating, the obturator arrangement with respect to the suctionorifices. These sources of movement also have the advantage ofpotentially being fast acting and readily controllable both in terms ofwhen movement occurs, but also in terms of their stroke length—so thatthe extent of the throttling applied to the suction orifices can readilybe adjusted and controlled.

It will be appreciated that the obturator arrangement may include asingle slide which includes multiple rows of apertures to provide athrottling effect to all of the suction orifices of the suction brake,but may equally comprise more than one slide, each carrying one or moreapertures, in for example one or more rows. In the event that multipleslides are provided, these may be coupled to move as one unit, or may bearranged to move separately or grouped to move as separate “banks” ofslides. It is also possible to provide an obturator arrangement thateffects some only of the suction orifices,

As a variant of the arrangement of FIG. 4 , rather than providing anapertured body as the, or as an element, of the obturator arrangement,part of the obturator arrangement adjacent a suction orifice may befixed, with another part being moveable with respect to the fixed part.In such an obturator arrangement an aperture is in effect created byspacing apart the fixed and moveable parts of the obturator, andthrottling of a suction orifice by moving the moveable part to overlypartially the suction aperture. An obturator arrangement for a suctionbrake according to such an embodiment of the invention could comprisemultiple fixed and moveable parts to provide a throttling effect to themultiple suction orifices of the suction brake.

It will be appreciated that the obturator arrangements described withreference to FIG. 4 may be retrofitted to existing suction brakes,whether their suction is generated using the Bernoulli effect—e.g.Bernoulli plates, or by means of a suction pump. But equally, theprinciples could be applied to newly created or newly designed suctionbrakes.

FIG. 5 is a plan schematic view of the face of a suction brake which, inuse faces the sheet as it is braked, according to an alternativeembodiment of the invention. In this alternative configuration for theobturator arrangement, rather than a simple linear translation betweenthe obturator and the suction orifices a relative rotation occurs. Asbefore, the suction brake comprises a hollow body that defines a cavity,and a face of the hollow body defines the plurality of suction apertures(366) that communicate with the interior cavity. In the exampleillustrated in the Figure the face that defines the plurality of suctionapertures is recessed with respect to the surrounding surface, and therecess receives an obturator element, so that the exposed surface of theobturator element is effectively flush with the surrounding surface ofthe hollow body.

In the Figure, the obturator element 562 is circular when viewedorthogonally from the sheet feed path, and includes a pair of holes 564spaced and sized to match the openings of a pair of suction orifices366. In practice there would generally be multiple obturator elements,and each including one or more apertures to provide throttle control fora similar number of suction orifices. As shown, the circular obturatorelement is mounted in a corresponding circular recess in the body thatprovides the suction orifices, with the exposed surface of the obturatorelement flush with the surrounding surface of the body. In this way, theassembly of the obturator elements and the body provides a sheet-facingsurface that is effectively flat, reducing the risk that the surface ofthe suction brake will damage sheets during processing.

FIG. 5 shows the obturator element 562 rotated with respect to thesuction orifices so that the latter are partially throttled with respectto their fully open position. The portions of peripheries of the suctionorifices that are concealed by the obturator element 562 are shown asdashed lines, while the useable opening of the suction orifices areshown shaded.

The obturator elements may be displaced (rotated) with respect to thesuction apertures by means of a “rack and pinion” arrangement, with partof each obturator element carrying a toothed “pinion” arrangement(preferably provided integrally in the material of the obturatorelement, for example by machining or by moulding/casting) within thebody. With these teeth, a “rack” cooperates—a linear element carryingteeth. Alternatively, a “worm-drive” type of arrangement could be usedbetween a common worm drive shaft and co-operating formations on each ofthe obturator elements. Another alternative drive arrangement would usea common linear drive shaft that is translated tangentially with respectto each of the obturator elements, with each of the obturator elementsincluding a crank arrangement that converts linear movement of the driveshaft into rotation of the obturator elements.

With suitable design, any of these drive elements can provide a compactand efficient mechanism to produce the required reciprocating arcuatemovement of the obturator elements with respect to the suction orifices.As with the sliding obturator arrangement described previously, these“circular” obturator arrangements may be driven by a motor (electrical,pneumatic, hydraulic) or by a linear actuator (solenoid, hydraulic,pneumatic).

It will be appreciated that it may be more difficult to retrofit theobturator arrangements described with reference to FIG. 5 to existingsuction brakes than to retrofit those described with reference to FIG. 4.

In order to avoid waste of available suction it is preferred to providea seal between the obturator element(s) and a co-operating surface withrespect to which the obturator element moves—as shown schematically as370 in FIG. 3 .

Whichever obturator arrangement is used, its operation is synchronisedwith the processing operation being carried out at the processingstation with which the suction brake is associated—e.g. with the sheetprocessing machine for which the suction brake provides a retardingeffect to each sheet being processed. In the first stage of the brakingoperation the obturator arrangement preferably operates at the fullyopen position, with the obturator being triggered to a throttled(partially obstructing) position at the start of the second stage of theoperation. Adjustment of the timing of the starting point forobstruction, and of the degree of obstruction (throttling) appliedshould be informed by settings that are known to work when using a knownsuction brake. Where an obturator arrangement is retrofitted to anexisting suction brake, known suction settings should provide a verygood guide to initial settings.

The invention claimed is:
 1. A suction brake for use with a sheetconveyor configured to convey a succession of flat elements in sheetform along a conveying path between a first location and a secondlocation, the suction brake comprising: a hollow body having an interiorcavity and a face that defines a plurality of suction apertures thatcommunicate with the interior cavity; and an obturator arrangementcoupled to the hollow body and moveable with respect to the suctionapertures; the obturator arrangement being moveable between an openposition, in which the obturator arrangement exposes the suctionapertures to a maximum extent, and a restricted position, in which theobturator arrangement occludes the suction apertures to a maximumextent, wherein the hollow body comprises a Bernoulli device and thesuction apertures are provided by the Bernoulli device, and wherein theobturator arrangement is configured to undergo rotation when movingbetween the open and restricted positions.
 2. The suction brake of claim1, wherein the obturator arrangement is positioned between the face ofthe hollow body and the conveying path of the flat elements.
 3. Thesuction brake of claim 1, wherein for each of the suction apertures theobturator arrangement defines an obturator aperture, and in the openposition the obturator aperture fully exposes a corresponding suctionaperture.
 4. The suction brake of claim 3, wherein in the restrictedposition the obturator aperture only partially closes the correspondingsuction aperture.
 5. The suction brake of claim 3, wherein the obturatorapertures have a same size.
 6. The suction brake of claim 3, wherein theobturator apertures are regularly spaced.
 7. The suction brake of claim1, wherein the obturator arrangement is coupled to a crank arrangementconfigured to move the obturator arrangement between the open andrestricted positions.
 8. The suction brake of claim 1, wherein theobturator arrangement is operatively coupled to one or more pneumatic,electric, or hydraulic motors configured and arranged to rotate to movethe obturator arrangement between the open and restricted positions. 9.The suction brake of claim 1, wherein the obturator arrangement includesa plurality of elements each configured and arranged to cooperate with adifferent one of the plurality of the suction apertures.
 10. A sheetconveyor system configured to convey a succession of flat elements insheet form along a conveying path between a first location and a secondlocation, the sheet conveyor system comprising: the suction brakeaccording to claim 4, the suction braking being arranged to apply arestraining force to trailing edges of flat elements being conveyed bythe sheet conveyor system.
 11. The sheet conveyor system of claim 10,wherein the sheet conveyor system is arranged to supply the successionof flat elements to a sheet processing device, and the suction brake isarranged to apply the restraining force to flat elements arriving at thesheet processing device.
 12. The suction brake of claim 1, wherein theobturator arrangement includes a plurality of holes, that expose andocclude the suction apertures, each hole comprising a hole interior facewith a conical profile, and a suction aperture interior face of each ofthe plurality of suction apertures has a conical profile and matches theconical profile of the hole interior face.
 13. The suction brake ofclaim 12, wherein the conical profile of the suction aperture isnarrower at a hollow body end of the suction aperture and wider at anobturator arrangement end of the suction aperture.
 14. The suction brakeof claim 1, wherein the size of the suction orifices is adjustable. 15.The suction brake of claim 1, wherein the obturator arrangement isinterchangeable.
 16. A method of applying a retardation force to amoving sheet of material using a suction brake having at least oneconical suction orifice, the method comprising: using the at least oneconical suction orifice to withdraw air from between the sheet ofmaterial and a surface of the suction brake; and subsequently throttlingthe at least one conical suction orifice to reduce a free area of the atleast one suction orifice; and subsequently using the reduced free areaof the at least one conical suction orifice to continue suction betweenthe sheet and the surface of the suction brake to cause the sheet toadhere to the surface.
 17. The method of claim 16, wherein the at leastone conical suction orifice includes a plurality of suction orifices,and the throttling is applied to each conical suction orifice of theplurality of conical suction orifices.
 18. The method of claim 16,wherein the method is applied to moving sheets of material beingsupplied to a sheet processing device.
 19. The method of claim 16,wherein the reduction of the suction is the same over an entire width ofthe sheet when moving the sheet.